|This process can be categorized as similar to that of permanent mold method, Here as the molten metal is being poured, a permanent metal mold revolved about its axis at high speeds ranging from 300 to 3000 rpm. This can be in horizontal, vertical or inclined positions. As a result, the molten metal is centrifugally thrown towards the inside mold wall. There is solidifies after cooling. It’s usually a fine grain casting with a very fine-grained pouter diameter.
Molds for Centrifugal castings can be divided into three types:
· The Permanent Mold: Made of steel, iron or graphite. Inside surface is coated with a thin refractory wash to increase mold life. The mold is preheated before coating, so as to dry the coating and improve the adherence to the mold surface.
· Rammed Mold: It consists of a steel metal flask, lined with a layer of refractory molding mix. The inside lining is coated with a refractory wash which is baked until dry and hard.
· Spun or Centrifugally Cast Mold: In the metal flask a predetermined mass of refractory materials in slurry form is poured.
The flask on rotation makes the refractory materials centrifuged onto the wall of the flask. The rotation is stopped and the liquid portion of the slurry drained off. It leaves the mold with a refractory coating, to be baked until dry before use.
Features of Centrifugal Casting:
· Castings can be made is almost any length, thickness and diameter.
· Different wall thicknesses can be produced from the same size mold
· Eliminated the need for cores.
· Resistant to atmospheric corrosion, a typical situation with pipes.
· Mechanical properties of centrifugal castings are excellent
· Only cylindrical shapes can be produced with this process.
· Size limited are up to 3m (10 feet) diameter and 15m(50 feet) length
· Wall thickness range from 2.5mm to 125 mm (0.1-5.0in)
· Tolerance Limit : On the OD can be 2.5 mm (0.1 in ) on the IS can be 3.8mm(0.15in)
· Surface finish ranges from 2.5 mm to 12.5 mm(0.1 -0.5in)rms